For me, personally, directly, "official discovery" is a non-event. As a knower, I ... know. I don't have an agenda of proof. I don't have a list of people to call and say "I told you so." So in the OP's scenario, I guess I'd finish breakfast and go to work same as any other day.
I reckon there'd be some talk at the water cooler. I reckon the "bleebers" would be talkin' "told ya so" and the scoftics (yep, we have them, too) would be sayin' "hoax" ... and nothing would have changed. I'm sure a few people would come to me to ask what I thought and I'd have to tell them "yep, they're real, but I'm not sure about that particular piece of evidence, it can stand or fall without affecting the truth." Hopes have been raised and dashed too many times. Nobody but the greenest noob is going to hang their personal belief on the legitimacy of one piece of evidence and ignore all others. In some matter of weeks - months - years, then I suspect it'd be just matter of fact. The scoffers might have even forgot they'd scoffed (and hoped everyone else had, too).
Public .. I reckon will be interested, at least 'til something else newsworthy comes along. The news-watching public has the attention span of a gnat. The bigger impacts will come from the lunatic fringe of various religions (both pro and con), political groups who want to adopt the big guys as their poster child for whatever the cause of the moment is, and so on.
I don't know what they are. I'm not CERTAIN of what's best so far as protection. I do have some ideas, but that's all they are, ideas. I suspect the very best that could come out of "proof" is if in that moment of shock we change course. I don't think most of the harm we do comes from malice, it comes from ignorance, "not my problem", and "don't give a ****." Perhaps their discovery could motivate us, inspire us to do the things we should be doing anyway. As it is, we can't look past our immediate gratification to consider that's in our own long term best interest and do something about it. If anything good comes from "discover" of the big guys, that would be the best.
Maybe we could learn respect. Gotta respect yourself before you can respect others. Look for bigfoot, find yourself. Dare we look in the mirror they show us?
MIB